- Terminal differentiation in skin is associated with the movement of keratinocytes out of the basal layer. Although events mediating commitment of keratinocytes and differentiation are not fully understood, changes in the adhesive properties are associated with the differentiation process. In vitro suspension of keratinocytes induces markers of both differentiation and apoptosis. Recent reports support the notion that apoptosis may play a central role in the pathogenesis of certain skin diseases such as psoriasis, basal cell carcinoma, and squamous cell carcinoma. The goal of the proposed research is to determine whether apoptosis is tightly coupled to, or an integral part of, normal keratinocyte differentiation. The state of differentiation and adhesion characteristics of cells undergoing apoptosis will be determined in normal human keratinocytes and an immortalized human keratinocyte cell line. Three specific aims will be addressed; 1) Characterize the presence and degree of apoptosis in cultured keratinocytes expressing specific differentiation markers after suspension-induced differentiation and in stratified cell layers of organotypic cultures; 2) determine whether disruption of integrin or cadherin-mediated cell adhesion signals keratinocytes to undergo apoptosis, and 3) characterize expression of the survival gene DAD1 in normal and diseased skin by in situ hybridization and immunohistochemistry to determine whether reduced expression observed during suspension-induced differentiation occurs in situ. Determine whether constitutive expression DAD1 alters suspension-induced differentiation and/or apoptosis in a human keratinocyte cell line.